The present application relates to an electrode including an active material layer, to a secondary battery using the electrode, and to a battery pack, an electric vehicle, an electric power storage system, an electric power tool, and an electronic apparatus that use the secondary battery.
In recent years, various electronic apparatuses such as a mobile phone and a personal digital assistant (PDA) have been widely used, and it has been demanded to further reduce the size and the weight of the electronic apparatuses and to achieve their long lives. Accordingly, as an electric power source for the electronic apparatuses, a battery, in particular, a small and light-weight secondary battery capable of providing high energy density has been developed.
In these days, it has been considered to apply such a secondary battery not only to the foregoing electronic apparatuses but also to other applications. Examples of such other applications may include a battery pack attachably and detachably mounted on the electronic apparatuses or the like, an electric vehicle such as an electric automobile, an electric power storage system such as a home electric power server, and an electric power tool such as an electric drill.
Secondary batteries utilizing various charge and discharge principles to obtain a battery capacity have been proposed. In particular, a secondary battery that obtains a battery capacity by utilizing insertion and extraction of an electrode reactant or precipitation and dissolution of an electrode reactant has attracted attention, since such a secondary battery provides higher energy density than a lead battery, a nickel-cadmium battery, and the like.
The secondary battery includes a cathode, an anode, and an electrolytic solution. The cathode includes a cathode active material layer provided on a cathode current collector, and the cathode active material layer contains a cathode active material engaging in a charge-discharge reaction. The electrolytic solution contains a solvent and an electrolyte salt. Since the configuration of the cathode and the composition of the electrolytic solution largely affect battery characteristics of the secondary battery, various considerations have been made on the configuration of the cathode, the composition of the electrolytic solution, and the like.
Specifically, in order to improve charge-discharge cycle characteristics and the like, a coat formed of a metal oxide such as BeO is provided on the surface of a cathode (for example, see Japanese Patent No. 3172388). In order to improve thermal safety and the like, the surface of a cathode active material is coated with a metal oxide such as an oxide of Mg (for example, see Japanese Patent No. 3691279). In order to improve charge-discharge efficiency and the like, a cyclic ester carbonate such as 4-methylene-1,3-dioxolane-2-one is contained in a nonaqueous solvent (for example, see Japanese Unexamined Patent Application Publication No. 2000-058122 and Japanese Unexamined Patent Application Publication (Translation of PCT application) No. 2010-533359).